In the art of underground sewer construction, the manholes which receive the sewer pipes are now usually pre-cast of reinforced concrete in a factory, with a base, one or more cylindrical risers and an upper section. For each installation it has been necessary for the engineers to specify to the factory exactly the location in the risers where the pre-cast portholes are to be located to receive the pipes. Not only is it time consuming and costly to cast such holes accurately in the risers, as they are centrifugally cast in the molds over the reinforcing framework, but an error in placement results in a commercially unacceptable product. In addition, upon delivery of such a manhole, with pre-cast portholes as ordered, to the site, it sometimes happens that the pipe in the ground is not properly aligned with the pre-cast portholes, thus causing time consuming fitting deep in a trench which is often wet.
Not only are pre-cast pipe holes difficult and costly to make in pre-cast risers, but the heretofore much used pipe joint and seal described in U.S. Pat. NO. 3,348,850 to Scales of Oct. 24, 1967, calls for the pre-casting of a plurality of threaded inserts around the outside of such a pre-cast hole. In using this type seal, the inner face of the pre-cast hole cannot be cylindrical, but must be tapered to receive a compressible O-ring, which is compressed by a bolt tightened ring of rigid material against the tapered face, such operation depending on the accuracy of the emplacement of the threaded inserts.
To produce a pipe-to-manhole joint not requiring threaded inserts, metal flange rings and compressed O-rings, it has been proposed to provide a flexible manhole sleeve with a serrated flange at one end cast, or embedded, in the inner wall of the pre-cast porthole and having the other end sleeved around and strap clamped around the pipe. Not only has it been costly and time consuming to position such a flange for casting into the riser, but the embedment of the flange may tend to weaken the wall, while the permanent anchoring of the flange prevents easy replacement in case of damage in transit or on the site.